The present invention relates to a concurrent control method for a communication device embedded with Wi-Fi Direct, and more particularly, to a concurrent control method to handle network scheduling and power saving when the communication device acts as a peer-to-peer (P2P) group owner and at the same time connects with a conventional wireless local area network (WLAN) access point (AP).
Wi-Fi Direct is a wireless communication protocol that allows Wi-Fi devices to communicate with each other without connecting to a traditional WLAN AP, which increases connectivity and a great number of P2P applications. Wi-Fi Direct is simply a software-only protocol and can be built into any Wi-Fi device. With a growing demand for Wi-Fi Direct application, the scenario of two or more protocols coexistence, e.g. a legacy WLAN protocol such as IEEE 802.11a/g/n coexisting with Wi-Fi Direct, or a 3G/4G protocol coexisting with Wi-Fi Direct, is applied in kinds of communication devices as laptops, smart phones and multimedia devices which are embedded with Wi-Fi Direct.
Please refer to FIG. 1, which is a diagram of a wireless network 10, including a WLAN AP 100, a communication device 102 which is embedded with a legacy WLAN protocol and Wi-Fi Direct as a laptop, and devices 104, 106 and 108 as a TV, a projector, or a digital camera. The left half of the wireless network 10 illustrates a traditional WLAN where the communication device 102 is a client station of a base service set (BSS) and can access the internet through the WLAN AP 100. The right half of the wireless network 10 illustrates a P2P network where the communication device 102 is a P2P group owner acting as an AP and connects with the devices 104, 106 and 108 as P2P client devices. The communication device 102 can access the internet through the WLAN AP 100 and use P2P services at the same time. In addition, the communication device 102 may connect with a Bluetooth embedded device or may access 3G/4G network and also use P2P services at the same time.
Timing synchronization function (TSF) is specified in IEEE 802.11 WLAN standards to achieve timing synchronization by periodically exchanging timing information through beacons. An AP in a BSS transmits beacons periodically to all client stations in the same BSS and each beacon includes a timestamp, which indicates the value of a TSF timer of the AP, and a beacon interval, which indicates the distance between two beacons. Beacons are sent at every target beacon transmission time (TBTT). Each client station in the BSS also maintains a local TSF timer counting in increments of microseconds, so they can miss a beacon and still remain roughly synchronized with the TSF timer of the AP. Upon receiving a beacon, a client station sets its local TSF timer to the timestamp included in the received beacon if the timestamp is later than its local TSF timer.
Please refer to FIG. 2, which is a diagram of beacon transmission of the communication device 102, illustrating beacons sent to P2P client devices and beacons received from the WLAN AP 100 in the condition that the P2P network and the BSS of the WLAN AP 100 operate on different channels, e.g. channel 3 and channel 11. As shown in FIG. 2, the communication device 102 establishes the P2P network first and connects to the WLAN AP 100 later. Since the communication device 102 acts as an AP, it periodically sends beacons to the P2P client devices 104, 106 and 108 at every TBTT and sends broadcast/unicast frame (if any) after TBTT. After the connection with the WLAN AP 100 is established, the communication device 102 starts to listen to beacons from the WLAN AP 100 at TBTTs of the WLAN AP 100.
Note that, in the case of the communication device 102 implemented by a single MAC/PHY solution, the communication device 102 has to switch between channels if the established P2P network and the BSS of the WLAN AP 100 operates on different channels. However, as shown in FIG. 2, when TBTT of the WLAN AP 100 is close to TBTT of the communication device 102, the communication device 102 is unable to switch from channel 3 to channel 11 to receive beacons from the WLAN AP 100 because it needs time to send beacons and broadcast frames to P2P client devices. As a result, the connection with the WLAN AP 100 may be suffered from the increasing of buffered packet delay time due to the lost of WLAN AP's beacon. On the other hand, if the communication device 102 switches from channel 3 to channel 11 to listen to beacons and broadcast frames sent from the WLAN AP 100, P2P network performance degrades due to information leakage.
Therefore, when the WLAN AP establishes the WLAN connection with the communication device 102 by using a channel different from the communication device uses to establish P2P network, it is hard to do fast network scheduling on an overlapping period of the broadcast frames of the communication device 102 and the WLAN AP 100.
Please refer to FIG. 3, which is a diagram of beacon transmission of the communication device 102 in the condition that the P2P network and the BSS of the WLAN AP 100 operate on the same channel, e.g. channel 6. Similar to the illustrated in FIG. 2, the communication device 102 establishes the P2P network first and then connects to the WLAN AP 100. As shown in FIG. 3, TBTT of the WLAN AP 100 is far away from TBTT of the communication device 102, and the communication device 102 has to wake up to listen beacons during each period of the power saving mode of a P2P group owner. Thus, power consumption increases. Besides, if the communication device 102 is also embedded with a TDMA-based protocol, TBTT of the communication device 102 may collide with an important time slot when it communicates with a TDMA-based communication device after the P2P network is established.
Therefore, concurrent operation of Wi-Fi Direct and a traditional WLAN protocol or a TDMA-based protocol is a major consideration to improve Wi-Fi Direct application.